A screen printing apparatus is known from JP-A-5 (1993)-57870 and U.S. Pat. No. 5,947,022 (Jul. 9, 1999), for example. In the screen printing apparatus of this type, a pair of scrapers or blades is provided inside the apparatus main body so as to be inclined inward and opposed to each other. Solder paste accommodated inside the main body is pushed out of the opening opened between the scrapers or blades with air pressure or discharge pressure produced by rotation of a rotary body, and screen printing is performed by fluid pressure of the paste discharged from the discharge opening. A surplus of the paste is collected by scraping it with one of the pair of scrapers or blades that follows the other during screen printing.
In the screen printing performed by using such a known type of screen printing apparatus, it is unavoidable that the liquid flux including solder particles leaks out from between the scrapers or blades and a screen during printing and remains on the screen for, for example, the following reasons: a desired number of printing operations are repeated automatically; in general, screens have deformed portions and small asperity; and solder particles and flux as components of the solder paste tend to be separated from each other by shearing force generated by the discharge pressure exerted on the solder paste during printing. Therefore, to obtain good printing results, it is necessary to frequently clean and remove the paste residue adhered to the screen manually or with a cleaning device. In this case, the paste residue removed from the screen is disposed of as wastes. However, solder paste is as expensive as 50,000 to 300,000 yen per 100 g and accordingly, disposal of reusable paste residue is uneconomical. Moreover, printing operations need to be suspended during a cleaning operation, which causes the efficiency of the printing operations to be lowered.
The present invention has been made to eliminate the drawbacks or disadvantages of the prior art as mentioned above.
It is, therefore, the main object of the present invention to provide a screen printing apparatus in which in each printing, a residual of the paste adhered to the upper surface of a screen in the preceding printing can be introduced and used for printing.
Another object of the invention is to provide a screen printing apparatus in which a paste accommodation chamber is provided inside the apparatus main body and the paste accommodated in the accommodation chamber is stirred and kneaded efficiently and sufficiently and discharged in the state in which its viscosity is adjusted so as to be suitable for printing.
A further object of the invention is to provide a screen printing apparatus which can be disassembled easily so as to be capable of facilitating cleaning and maintenance, inspection, or the like of main components such as the main body and a paste stirring unit.
Other objects of the invention will become apparent from the description which will be made in respect of its embodiments hereinafter.